FIG. 4 is a view showing a conventional start-and-stop control device for a gas turbine and FIG. 5 is a view showing a starting sequence to be carried out by the start-and-stop control device.
As shown in FIG. 4, a gas turbine 1 includes a gas turbine body 2 together with a combustor 3, a compressor 4, an exhaust gas duct 5, a tachometer 13, a start-and-stop control device 14, and the like. A rotating shaft 6 of the compressor 4 is coupled with an unillustrated rotating shaft of the gas turbine body 2 and the compressor 4 compresses outside air (air) which is taken in by rotation together with the gas turbine body 2. The combustor 3 generates a combustion gas for rotating the gas turbine body 2 by combusting a fuel gas together by the compressed air supplied from the compressor 4, and supplies this combustion gas to the gas turbine body 2. The combustion gas after flowing through the gas turbine body 2 is discharged through the exhaust gas duct 5 provided in a rear portion of (on a downstream side of) the gas turbine body 2. This discharged combustion gas is subjected to heat recovery by an unillustrated heat recovery steam generator (HRGS) and is then emitted from an unillustrated stack to the atmosphere.
The tachometer 13 measures the number of revolutions of the gas turbine body 2 and outputs a signal of this measured number of revolutions to the start-and-stop control device 14. Meanwhile, a rotating shaft 8 of a power generator 7 is also connected to the rotating shaft 6 of the compressor 4. Therefore, the power generator 7 rotates together with the gas turbine body 2, and thereby generates power.
A tip end side (a downstream side) of a fuel gas pipe 9 is connected to the combustor 3 and a fuel gas shutoff valve 10 is provided in a mid portion of this fuel gas pipe 9. Meanwhile, a tip end side (a downstream side) of a nitrogen gas pipe 11 is connected to the fuel gas pipe 9 and a nitrogen gas shutoff valve 12 is provided in a mid portion of this nitrogen gas pipe 11. Abase end side (an upstream side) of the nitrogen gas pipe 11 is connected to an unillustrated nitrogen gas supply device. Moreover, a base end side (an upstream side) of the fuel gas pipe 9 is connected to an unillustrated blast furnace in an iron works, and when the fuel gas shutoff valve 10 is opened, a blast furnace gas discharged from the blast furnace is supplied to the combustor 3 through the fuel gas pipe 9. That is, the blast furnace gas is used as the fuel gas in the gas turbine 1 of the illustrated example.
Moreover, this blast furnace gas contains carbon monoxide as a main component. Accordingly, when the gas turbine 1 is stopped for periodic inspection or the like, it is necessary to purge the uncombusted fuel gas (blast furnace gas) that remains in the gas turbine body 2 and the like. Moreover, when the gas turbine 1 is started, if the uncombusted fuel gas (blast furnace gas) remains in the exhaust gas duct 5 and the like, there is a risk that the fuel gas is heated by the combustion gas and is combusted inside the exhaust gas duct 5 and the like. Accordingly, it is necessary to purge the fuel gas, before starting the supply of the fuel gas to the combustor 3 and performing ignition. For this reason, the start-and-stop control device 14 performs the following gas turbine stop control and gas turbine start control.
<Gas Turbine Stop Control>
Although illustration is omitted (see FIG. 2), in stopping the gas turbine, the fuel gas shutoff valve 10 is closed, and then the nitrogen gas shutoff valve 12 is opened just for a predetermined time period. As a result, the uncombusted fuel gas remaining in the fuel gas pipe 9, the combustor 3, the gas turbine body 2, and the exhaust gas duct 5 is pushed out by the nitrogen gas that is supplied from the nitrogen gas supply device through the nitrogen gas pipe 11.
<Gas Turbine Start Control>
On the other hand, in starting the gas turbine, the gas turbine body 2 is accelerated until reaching the number N of revolutions for ignition (such as 600 rpm) as shown in FIG. 5 by rotation driving means (not shown) such as an auxiliary motor and is maintained at this number N of revolutions for ignition. At this time, since the compressor 4 is also rotated with the gas turbine body 2, the air compressed by this compressor 4 will flow into the combustor 3, the gas turbine body 2, and the exhaust gas duct 5.
Accordingly, when the start-and-stop control device 14 judges that the number of revolutions of the gas turbine body 2 rotated and driven by the rotation driving means reaches the number N of revolutions for ignition at a time point T1 based on a signal of this measured number of revolutions from the tachometer 13, a closed state of the fuel gas shutoff valve 10 is maintained from this point until a predetermined time period ΔT (a period until a time point T2) passes. As a result, when the uncombusted fuel gas remains inside the gas turbine 1 (such as the exhaust gas duct 5), the remaining fuel gas is pushed out by the compressed air from the compressor 4 which is rotating at the number N of revolutions for ignition together with the gas turbine body 2. That is, exhaust gas duct purge is carried out. Here, a judgment as to whether or not the predetermined time period ΔT has passed is made by a timer included in the start-and-stop control device 14.
Thereafter, when judging that the predetermined time period ΔT has passed at the time point T2, the start-and-stop control device 14 supplies the fuel gas to the combustor 3 by opening the fuel gas shutoff valve 10 and performs ignition with an ignition plug. Accordingly, the gas turbine body 2 is rotated and driven by the combustion gas generated by the combustor 3 thereafter and is accelerated until reaching a rated number of revolutions (such as 3600 rpm).
Here, the following is a prior art document describing the purge of the uncombusted fuel.
Patent Document 1: JP-A 59-18240